An organic EL display panel is a display panel including a light emitting element which uses electroluminescence of an organic compound. In other words, the organic EL display panel has an EL apparatus which includes a cathode, an anode, and an organic compound which is disposed between both the electrodes and performs electroluminescence. The organic compound which performs electroluminescence may be largely classified into a combination of low-molecular organic compounds (including a host material and a dopant material) and a high-molecular organic compound.
Examples of the high-molecular organic compounds performing electroluminescence include polyparaphenylene vinylene called PPV or derivatives thereof, and the like. An organic EL display panel using the high-molecular organic compound performing electroluminescence can be driven at a relatively low voltage and thus has a feature in which power consumption is low. In addition, the high-molecular organic compound can be provided as ink by dissolving the high-molecular organic compound in an aromatic organic solvent such as xylene or toluene. The providing of ink enables an organic emission layer to be formed using a printing method such as an ink jet method, is regarded as being capable of handling a large-sized screen of a display panel, and is thus currently positively researched and developed.
The organic EL apparatus is a laminate apparatus formed by laminating a plurality of layers such as an electrode, a hole injection layer, and an organic emission layer. A film thickness of each layer is a very important factor in emission characteristics of the organic EL apparatus. Among them, the organic emission layer which directly contributes to emission is required to have high film thickness uniformity. This is because a disparity of the film thickness leads to luminance unevenness or emission color unevenness, and finally leads to poor display quality. For this reason, a technique is known in which an organic emission layer is formed on a planarized ground (for example, refer to PTLs 1 and 2).
When the organic emission layer is formed using a printing method such as an ink jet method, an ink is coated in a region defined by barrier walls called banks, a solvent in the inks is dried so as to form an organic emission layer with a film thickness of about 100 nm. A film shape of the organic emission layer is determined depending on factors such as a coating method, physical properties (the boiling point, a viscosity, and the like) of an ink, physical properties (wettability, film thickness, taper angle, and the like) of a bank, and a drying condition of the organic emission layer ink. Therefore, if the ink drying condition is changed, a film shape of the organic emission layer is also changed.
For example, the concentration of solvent vapor of the ink is low in an outer circumferential portion of the panel, and thus drying of the ink is promoted. Therefore, drying speed of the ink is low in a central portion of the panel, and drying speed of the ink is high in the outer circumferential portion of the panel. For this reason, the organic emission layer of a pixel located on the outer circumferential side of the panel is inclined outward, and thus a film shape worsens (refer to PTL 3). Particularly, if a panel increasingly has a large size, a difference in drying speed becomes notable in the central portion and the outer circumferential portion of the panel, and thus a film shape of the organic emission layer tends to further worsen in the outer circumferential portion of the panel.
In order to solve this problem, a technique is known in which an element (hereinafter, referred to as a “light emitting element”) contributing to emission is disposed in the central portion of the panel, and a non-emissive element is disposed in the outer circumferential portion of a substrate (refer to PTLs 4 to 10). The element with a bad film shape in the outer circumferential portion of the panel does not emit light, and only the element in the panel central portion with good thickness uniformity emits light. Thereby, it is possible to provide an organic EL display panel in which luminance unevenness or emission color unevenness is smaller, and thus display quality is better than an organic EL display panel which does not include a non-emissive element.
FIG. 1A is a plan view of an organic EL display panel disclosed in PTL 5, and FIG. 1B is a cross-sectional view taken along the line M-M′ of the organic EL display panel shown in FIG. 1A. As shown in FIGS. 1A and 1B, the organic EL display panel disclosed in PTL 5 includes effective emission region A in which light emitting elements 111 are arranged, and dummy region B in which non-emissive elements 111′ are arranged. As such, the outer circumferential portion of the panel in which a film shape of an organic functional layer is bad is used as dummy region B, and the central portion of the panel in which a film shape of the organic functional layer is favorable is used as effective emission region A. Thereby, it is possible to provide an organic EL display panel in which there is no luminance unevenness or emission color unevenness, and thus display quality is good.
In addition, as shown in FIG. 1B, light emitting element 111 has a contact hole, but non-emissive element 111′ does not have a contact hole.
However, in the organic EL display panel shown in FIG. 1, as disclosed in PTL 5, however large the dummy region was, a film shape of the organic functional layer of the light emitting element located at an edge of the effective emission region could not made to be favorable (refer to Comparative Example).
For this reason, in the organic EL display panel as disclosed in PTL 5, luminance unevenness or emission color unevenness occurs between the light emitting element of the edge of the effective emission region and the other light emitting elements, and thus display quality is low.
On the other hand, an organic EL apparatus is known in which a dummy region where a dummy pixel (non-emissive element) is disposed is provided around an effective emission region where an effective pixel (light emitting element) is disposed, and the dummy pixel is formed in the same manner as the effective pixel except for being electrically non-conducted (refer to PTLs 11 and 12). The dummy pixel of the organic EL apparatus has a contact hole in the same manner as the effective pixel.
The contact hole is formed in a planarized film. The planarized film is generally made of a resin. When moisture is contained in the planarized film through adsorption of the moisture or the like, there are cases where the moisture is diffused into other layers of the organic EL element. In addition, when the moisture enters an emission layer or a charge injection layer, emission characteristics may deteriorate. In the organic EL apparatus in which the contact hole is provided in the dummy pixel in the same manner as the effective pixel, there is a necessity for consideration of the deterioration in the emission characteristics due to diffusion of moisture of the planarized film.